In the preparation of pressed board, i.e. a relatively rigid structure which can be pressed from various materials and bonded with the aid of natural or synthetic resins, it is not uncommon to apply flexible facing sheets to the upper surface or the lower surface of a core formed by the pressed board, thereby constituting a laminate. Facing sheets of various types may be employed. For example, the facing sheet may be a contoured and patterned layer which is applied to impart a desired pattern to the pressed board in the formation of so-called paneling or decorative pressed board. The facing sheet may also, if desired, be a sealing layer or a protective layer whose function it is to protect against wear and underlying layer, e.g. a patterned sheet of the type described. In all of these cases it is necessary, in forming a laminate of pressed board to apply a facing sheet to the press board or, more generally, to a stack.
The term "pressed board" is used herein to refer generally to all parts of fiber and particle boards, whether the latter are porous or impermeable to fluids or whether the bonding resins are naturally occuring materials present in the particles to be bonded together, or are synthetic resins which may be firmly activated to effect the bonding under heat and pressure.
In practically all cases, the laminate is subjected to pressure, e.g. in a platen press, and usually also to heating to activate the synthetic resin binder.
Typical material which can be used in particle and fiber boards for the aforedescribed purpose, are wood chips, saw dust, other wood particles, cellulosic and wood fibers, mixtures of cellulosic fibers and other fibers and the like. In addition, the laminate may include a pressed board of the aforedescribed type sandwiched between or having on one side thereof a layer of wood in the form of veneer. In this case, the particles or fiber board may be a core flanked between a pair of such veneers in the manner of plywood.
The binder which is customarily used can be the natural abietic resins of the wood particles or fibers or synthetic resins preferably of the thermally hardenable type such as melamine, phenolformaldehyde, resorcinol and urea resins.
With the process of the present invention any pressed board, particle board, fiber board or composite or sandwich board of the aforedescribed type may be used.
It has been proposed heretofore, in the manipulation of sheets, to provide a device for the handling of sheets which includes a device for removing a single sheet from a stack of such sheets, a manipulating drum having a fixing device for entraining the leading edge of a sheet fed from the aforementioned stack and carrying the sheet to a location remote from this stack, and a table or surface for assembling the laminate stack at the latter location, the sheet carried by the drum being generally fed with its leading edge foremost on the assembling table or surface. The fixing device on the drum can be a clamp or a suction head which can release the leading edge of the sheet as the latter approaches the assembly table, the advance of the sheet after release of the leading edge being effected by frictional engagement of the periphery of the drum with the sheet.
A pressing unit, e.g. a plurality of pressure rollers angularly spaced about the periphery of the drum, can be provided for holding the sheet against the drum periphery while the latter advances the sheet onto the assembly table after the fixing device has been released. Between the table and the drum, moreover, means can be provided for deflecting the sheet onto the table away from the periphery of the drum.
A device for manipulating sheets in the manner described has not been found to be effective for the application of facing sheets to pressed board in all instances and these devices are, therefore, more generally used for the handling of paper sheets, synthetic foil sheets or the like in connection with printing plants or plants for the fabrication of bags or sacks.
One of the problems encountered in attempting to use such a device for the handling of facing sheets in connection with the fabrication of faced particle board, fiber board or the like resides in the fact that the sheets can only be applied in one sense to the stack, i.e. to the upper face of the sheet as it is removed from the stack being applied to the assembly cable with its upper face in the same orientation. Thus when it is desired to apply a facing sheet at the bottom of the stack with its upper face turned downwardly and a sheet at the top of the stack with its upper face turned upwardly, the device or apparatus described is not satisfactory.
Typical facing sheets or overlays for pressed board are asymmetrical, i.e. have a synthetic-resin impregnated surface which must be turned toward the pressed board so that, upon the application of heat and pressures to the laminate, the synthetic resin impregnated side bonds to the remainder of the stack or laminate. This underscores the importance of being able to apply these sheets with alternating orientation to the assembly table since, if upper and lower facing sheets are to be applied, they must be oriented oppositely so that at all times the synthetic resin impregnated side of the facing sheet contacts the core of the pressed board.